1. Field of the Invention
The invention relates to the preparation of 1,6-octadiene by the reductive dimerization of 1,3-butadiene with formic acid and more particularly relates to such a process conducted in the presence of a platinum catalyst and a solid polymeric amine promoter.
2. Other Processes in the Field of the Invention
Linear dimerization of butadiene (1,3-butadiene) provides a source of C.sub.8 unsaturated hydrocarbon intermediates useful for the synthesis of diacids, diesters, diols or diamines. Linear oligomerization of butadiene typically results in the formation of n-octatriene products, and in particular either 1,3,6-octatriene or 1,3,7-octatriene. Unfortunately, such compounds are unreactive in many reactions or give complex reaction mixtures. 1,7-Octadiene is also a common product. However, 1,6-octadiene is another typical product. It may be used in the production of decanediol or 1,7-octadiene. A typical problem in these dimerization methods is that a variety of products are produced. It is desirable to discover systems which yield primarily one substance.
The dimerization of olefins is a well known reaction. U.S. Pat. No. 3,562,351 describes a method for dimerizing and co-dimerizing monoolefins in the presence of a Group VIII water-soluble metal salt which is activated by treatment with an organometallic compound. The Group VIII metal is preferably nickel, cobalt or mixtures thereof. A rhodium catalyst is useful in synthesizing dienes from alphamonoolefins and conjugated dienes according to U.S. Pat. No. 3,565,821. Further, U.S. Pat. No. 3,848,015 teaches the production of dimers and trimers using a carbonyl moiety-free complex of a transition metal of Group VIII and an electron donor. The Group VIII transition metal is listed as being iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, although the preferred metals therein are iron, cobalt and nickel, nickel being especially preferred. Dimerization of diolefins may also be effected by maintaining the olefins in inert solvent solution in contact with a catalyst which is the product of the interaction between two metal complexes, each of which is a nitrosyl and/or carbonyl ligand, as seen in U.S. Pat. No. 3,917,730.
A general review of butadiene telomerization is given by R. Baker in ".pi.-Allylmetal Derivatives in Organic Synthesis", Chemical Reviews, Vol. 73 (1973), No. 5, pp. 491-493. Transition metal catalysts mentioned therein include triallyl cobalt, Co.sub.2 (CO).sub.8, cobalt(II) chloride, cobalt acetylacetonate, ferric acetylacetonate, ferric chloride, nickel chloride, .pi.-allylpalladium chloride and (Ph.sub.3 P).sub.2 Pd (maleic anhydride).sub.2. Tetrakis(triphenylphosphine)platinum is also mentioned as yielding mainly vinyl cyclohexene from the dimerization of butadiene in benzene solution.
Palladium catalysts are particularly popular for the co-dimerization of 1,3-butadiene and ethylene. U.S. Pat. No. 3,920,763 employs a .pi.-allyl complex catalyst for this purpose which comprises a palladium source, a monotertiary phosphine electron donor ligand, a combination reducing agent and Lewis acid and an acidic, solid, silica-based support material. A dienophile-coordinated palladium-phosphine complex such as bis-(triphenylphosphine)-(maleic anhydride) palladium is the preferred catalyst for co-dimerization and homo-dimerization of butadienes in U.S. Pat. No. 3,925,497.
European patent application No. 0004408 teaches the preparation of 1,7-octadiene by the hydrodimerization of butadiene using a palladium-organophosphine catalyst which has been pre-treated with a reducing agent. The reducing agent may be formic acid, the triethylamine salt of formic acid, hydrazine, hydrogen or carbon monoxide. Palladium acetylacetonate is mentioned as a suitable palladium catalyst. Amine solvents may be used and carbon dioxide is taught as being able to increase the butadiene conversion. Two recent patents to Pittman, U.S. Pat. Nos. 4,243,829 and 4,377,719, and J. Mol. Cat., Vol. 15 (1982), pp. 377-381 reveal processes for preparing 1,7-octadiene selectively by dimerizing butadiene in the presence of a catalytic amount of palladium and a tertiary phosphine including a solvent, a strong base and formic acid.
Certain platinum catalysts have also been shown to be useful in butadiene dimerizations. L. H. Slaugh, et al. in "A Novel Effect of Carbon Dioxide on Catalyst Properties. Dimerization of Butadiene", Journal of the American Chemical Society, Vol. 91, No. 21 (1969), pp. 5904-5, disclose that the presence of carbon dioxide enhances the yield to 1,3,7-octatriene over platinum, palladium and nickel catalysts. The metals are complexed with triphenyl phosphines and occasionally carbonyls. Platinum catalysts such as lithium tetrachloroplatinate(II) and Pt(C.sub.5 H.sub.7 O.sub.2).sub.2 are used to make 1,7-octadiene from butadiene in the presence of dimethylformamide and formic acid as described in S. Gardner, et al., "Platinum-Metal Catalyzed Formation of Linear Octadienes", Tetrahedron Letters, No. 2 (1972), pp. 163-164. However, the selectivity to 1,6-octadiene is unsatisfactory.
U.S. Pat. No. 3,732,328 teaches the production of an octadiene selected from the group consisting of octa-1,6-diene, octa-1,7-diene, monomethylocta-1,6-diene, monomethylocta-1,7-diene, dimethylocta-1,6-diene and dimethylocta-1,7-diene. Butadiene and/or isoprene at a temperature of 20.degree. to 200.degree. C. is contacted with a 10.sup.-1 to 10.sup.-5 molar concentration of a platinum, palladium or ruthenium catalyst, such as halides, alkanoates, acetylacetonates, bisbenzonitrile palladium(II) and lithium palladous chloride. Formic acid and a polar solvent must also be present. Dimethyl formamide is a preferred solvent. However, this process suffers from a low yield to 1,6-octadiene.
Similarly, U.S. Pat. No. 3,823,199 teaches that 1,6- and/or 1,7-octadienes may be produced by reacting 1,3-butadiene with metallic platinum, palladium, rhodium, ruthenium or osmium in the presence of formic acid. Preferably, a compound of one or more of these catalysts in a non-polar solvent such as benzene is employed. Selectivities to 1,6-octadiene are not disclosed, and no amine promoter is used.
S. Teranishi in J. Org. Chem., Vol. 46 (1981), pp. 2356-2362, discloses a palladium(O) complex supported on a phosphinated polystyrene as a catalyst for the reaction of 1,3-butadiene and formic acid. In this case, 1,7-octadiene was produced exclusively.
Finally, U.S. Pat. No. 4,334,117 reveals an improved process for the preparation of alkadienes by contacting butadiene or isoprene with a platinum or palladium catalyst, optionally in a sulfolane solution, in the presence of a tertiary lower alkylamine formate and at least one particularly-defined phosphine compound. Platinum acetylacetonate is specifically mentioned.
Given the methods noted above, it would still be desirable to discover a process providing high selectivity to 1,6-octadiene with ease of subsequent separation.